The invention relates to a method of producing magnetite by culturing a microorganism designated GS-15 in the presence of organic matter and ferric iron.
Magnetite (Fe.sub.3 O.sub.4) is a mineral of great commercial value in that it is useful, e.g., in magnetic recording devices and as toner for plain paper copiers. Particularly desirable for these purposes is magnetite in ultrafine-grained (roughly 20-50 nanometers in diameter) form. It has recently been discovered that biologically pure cultures of a magnetotactic bacterium designated "MS-1" can be used to synthesize ultrafine-grained magnetite. In U.S. Pat. No. 4,385,119 (Blakemore), it is disclosed that a magnetotactic bacterium of the genus Aquaspirillum contains intracellular chains of single domain magnetite particles, and that these particles can be recovered from cultures of the bacterium and employed for the purposes described above. Methods of culturing the magnetotactic bacteria and removing the products produced therein are disclosed in U.S. Pat. No. 4,394,451 (Blakemore et al) and U.S. Pat. No. 4,677,067 (Schwartz et al), respectively.
Unfortunately, the method of producing useful magnetite particles through culturing microorganisms as described in the above patents is extremely impractical for a number of reasons. First, these organisms are very difficult to culture in large quantities. Second, the amount of magnetite produced in each cell is extremely small (only about 20 crystals), and this further limits the total amount of magnetite that can be recovered. Third, under processes carried out with magnetotactic bacteria, the oxygen tensions which are applied to the culturing medium have to be very carefully controlled in order to ensure that only magnetite-bearing bacteria will be cultured. Finally, the magnetite crystals are produced intracellularly in bacterium MS-1 and as such will stay bound within the organism, thus requiring extensive purification and recovery procedures in order to obtain pure magnetite.
It would thus be desirable to develop a microbial process which produces ultrafine-grained magnetite extracellularly so that it is readily separable and recoverable from a culture medium. It is also desirable that the microbe used in such a process be able to produce copious qualities of magnetite, and that such a microbe be readily grown in mass culture using inexpensive materials.